Congrats! I'm sure your kid is happy. If you want to drop weight, check the tires. I was able to drop 1 lb just by swapping out the stock tires. You will also find the cranks and BB to be on the heavy side. Good luck. We're heading up to MT. Laguna on Sunday if you want to give it a run.

1) replace the bottom bracket, that will save some weight.
2) handlebars - any riser bar will work you'll just have to cut it down. Two things to consider: 1) be sure to buy a bar that works with the existing stem (that is if you're going to keep the stem); and 2) if the seat height is already lower than the bars you may want to go with a flat bar instead of a riser, adding a riser bar that increases the bar height will make the bike feel too "chopper" like. I used a FSA XC190 riser bar for my son's bike, it's alloy (so it was cheaper than carbon) and was easy to cut down, and its relatively light.

3) Replacing the wheels is the best way to knock off some weight, but it will cost you. I purchased a set of 28-hole hubs and SunRingle rims on eBay and had them built by a local shop. This saved considerable weight, but I also had to buy a 9 speed cassette, new rear derr. and a set of new shifters. Works way better, but cost lots.

If you want to drop weight, check the tires. I was able to drop 1 lb just by swapping out the stock tires. You will also find the cranks and BB to be on the heavy side. Good luck. We're heading up to MT. Laguna on Sunday if you want to give it a run.

Thanks! We are planning to go to Mt. Laguna in two weeks to camp and will ride the trails, thanks.

Originally Posted by ThornPatch

2) if the seat height is already lower than the bars you may want to go with a flat bar instead of a riser.

Her seat is a little lower than her handle bars, however she is used to them being a little higher.

Originally Posted by ThornPatch

3) Replacing the wheels is the best way to knock off some weight, but it will cost you. I purchased a set of 28-hole hubs and SunRingle rims on eBay and had them built by a local shop. This saved considerable weight, but I also had to buy a 9 speed cassette, new rear derr. and a set of new shifters. Works way better, but cost lots.

That is good to know, both what is possible and that it is expensive.

This bike is perfect for where my daughter is as far as riding skill, height, strength, etc. I was planning on waiting for a 24" diameter wheeled bike, but she would not be ready for that for at least a year. Even with this bike she is slowly getting used to shifting gears and the handle brakes. I will pass it on to my son, so I feel justified buying the bike.

Bill, I spent about $550 on a new custom built wheelset for my son's bike, which is crazy expensive for a 20" wheelset, but that price also included a new Sram 990 cassette, x-9 sort cage rear derr, and x-7 shifters. I built the bike for my 9 yr old, he's average hgt, and some might say I should have put him on a 24" bike, but since he likes to jump a lot he's better off on the smaller 20" wheels. The small wheels gives him more control over the bike, and boosts his confidence. Hopefully I can at least 2 -3 years out of it before he's ready for a bigger bike. Either way the parts can transfer over to a new bike pretty easily.

Bill, I spent about $550 on a new custom built wheelset for my son's bike, which is crazy expensive for a 20" wheelset, but that price also included a new Sram 990 cassette, x-9 sort cage rear derr, and x-7 shifters. I built the bike for my 9 yr old, he's average hgt, and some might say I should have put him on a 24" bike, but since he likes to jump a lot he's better off on the smaller 20" wheels. The small wheels gives him more control over the bike, and boosts his confidence. Hopefully I can at least 2 -3 years out of it before he's ready for a bigger bike. Either way the parts can transfer over to a new bike pretty easily.

Thanks, I got your PM too. That really helps me out. Did you build the wheelset for better performance and/or weight reduction? I would spend that kinda money to make my daughter's bike better, if I know she is going to use it. My goal is to spend more time with my daughter doing stuff we both enjoy.
Thanks
Bill

Bill, I spent about $550 on a new custom built wheelset for my son's bike, which is crazy expensive for a 20" wheelset, but that price also included a new Sram 990 cassette, x-9 sort cage rear derr, and x-7 shifters. I built the bike for my 9 yr old, he's average hgt, and some might say I should have put him on a 24" bike, but since he likes to jump a lot he's better off on the smaller 20" wheels. The small wheels gives him more control over the bike, and boosts his confidence. Hopefully I can at least 2 -3 years out of it before he's ready for a bigger bike. Either way the parts can transfer over to a new bike pretty easily.

I did something similar to ThornPatch. Sun Envy Lite, XT hubs, Sapim dbl btd spokes. Cost was $280. Dropped a ton-o-weight. I reused my cassette and shifters from an older bike so I didn't have that cost. You can purchase 2010/11 Sram shifter/cassettes cheaper than 2012.

Is it possible to buy a Middleburn 140mm cranks, with a 32 chainring and bashguard? And a Irod 7 speed cassette, 15, 17, 21, 24, 28, and 32? That is considering the bike has a 34 and 42 chainrings and a different cassette? Thanks Bill

I used cranks from bikesmithdesign.com, he recommends much shorter than that, I believe he said 10% of height plus 5mm, max length on the cranks. Anyways, if you look at a serious kid specific bike manufacturer like islabikes.co.uk then you'll see their 20" models have cranks from 114-127mm max.
I downsized the stock 152mm cranks on my son's 24" bike to 137mm and have been really pleased with the outcome.
I got the race face bash guard on race face rings. The crankset looks awesome and he delivered it fast too! Well worth it, imo.

I calc'd 136.5 for my 51" tall girl. Thanks. I have read good things about bikesmith. Bill

If she is 51" she needs to ride 145-150mm length crank arms. I would go 145 conservative and 150mm for growth. For reference, my son is 48" tall and uses 140mm. The 10% thing is way off for kids. If you are planning on running a 1x setup, buy Sinz, redline or AC mini cranks ($50-70). If you need to run 2x/3x setup, bike smith will shorten cranks for a price. I like the 1x setup and personally run it on my mtn bike.

The right way to decide gear ratios is to review the numbers. Look at the gear ratios and decide where your kid will be able to operate best. Below are quick charts I did to show you some gear inch numbers. If you would like to know the roll out, multiply by pi (3.14).

The first chart shows a single speed gear inch setup for your 20" (15-32t setup). The next chart shows my son's 1x8 setup. And for comparison, the last chart shows 26" mtn bike gearing for 1x, 2x and 3x setups. For example, my 1x10 setup uses a 36 front and 11-36 rear cassette. My gear inches run from 25" to 83". My son uses a 35 front 12-32 rear cassette or 21" to 57". My son rarely uses his top 3 gears except on the occassional down hill but that usually involves more coasting, feet flat and looking way ahead (+20mph).

Based on the cassette that you want to run, 15-32, I would be a little worried about running out of steam on the upper (tougher) gears. Either increase the cog count or include a 13t in there. If you build custom wheels think about doing a 9 or 10 spd. This will solve most of your issues. Hope this helps.

Gear inch chart for 20" mtn bike 7spds

Gear inch chart for 20" mtn bike 8spds

Gear inch chart for 26" mtn bike (provided so you willl know what the level of effort is needed to push on a pedal per respective gear on your own bike).

Great info, thanks!! I was meaning to also ask, if I get the Schwalbe Mow Joes, I would get the 20 by 2 inches wide for the stock wheels and if I upgrade my wheels those tires should fit on say a sun envy lite, right?

Seems like the Mow Joes are not carried by many places? What are some good lightweight inner tubes?
Thanks
Bill

If she is 51" she needs to ride 145-150mm length crank arms. I would go 145 conservative and 150mm for growth. For reference, my son is 48" tall and uses 140mm. The 10% thing is way off for kids. If you are planning on running a 1x setup, buy Sinz, redline or AC mini cranks ($50-70). If you need to run 2x/3x setup, bike smith will shorten cranks for a price. I like the 1x setup and personally run it on my mtn bike.

I agree with this.
My 48" son has no problem spinning 140mm arms at high cadence. Anything shorter than 135 for him would be super awkward. The cranks on his 16" bike were ridiculously short and were the main reason I built him a 20".
+1 for Sinz and AC cranks. Good stuff.

Actually, after further thinking, I wouldn't go larger than 145mm on a 20" bike. At 51" she could ride either 145 or 150mm cranks but on a 20" bike you may get a lot of pedal/ground strikes. If she was on a 24" you could go larger.

I cut about 2.5 pounds by exchaning the spark with a scale. I did this a few days after I bought the spark. The LBS has great customer service!!

I let my daughter ride the bike around for the last month or so and decided what else I wanted to do.

I recently bought an IRD 13-32 freewheel in place of the Shimano 14-28. I cut off the big outer chainring that my daughter will never use. I bought a Paul Compents chain keeper, purple handle grips and a Shimano Trigger Shifter.

My daughter likes the improvements and it seems to help her confidence.

ideas

I got a fusion x air shock from the manufacturer. Big differences in adjustability. Had cranks cut down to 130. I also am getting a new wheelset built up. Stock they weigh 28 pounds with pedals. My goal is to get it sub 25.

I got a fusion x air shock from the manufacturer. Big differences in adjustability. Had cranks cut down to 130. I also am getting a new wheelset built up. Stock they weigh 28 pounds with pedals. My goal is to get it sub 25.

Great score getting the X-Fushion air shock. So nice having adjustable rebound damping so the rear end isn't a pogo stick. With this shock on the Spark its the best rear suspension you will find on a kids bike - works awesome.

x-fusion

Originally Posted by xc71

Great score getting the X-Fushion air shock. So nice having adjustable rebound damping so the rear end isn't a pogo stick. With this shock on the Spark its the best rear suspension you will find on a kids bike - works awesome.

Hi, where and how to buy X-fushion schock to scott spark jr? What is the cost?
I live in Poland, but I have friends in the U.S..
Thank you for your reply.

I picked up a Scott Scale Jr 20 for my son as well, I'm hoping to make a few improvements over time... are those Velocity Aeroheats really the best bet for at 20" rim? I'm thinking about picking up some Novatec or Circus Monkey hubs to build wheels.

What a difference

So I live in the mountains of NC and wanted my son to join me on some great rides. At this point, I am done. He has:
127mm custom cut Truvativ triple crankset from BikeSmith. In hindsight, I think 135 or so might have been better to give him room togrow. If anyone wants to buy these from me PM me.
X9 hubs with Velocity Aeroheat rims. Expensive upgrade ( I did find a bargain on the parts) but the way I look at it, when he outgrows this, I will relace the hubs with 24" rims and ebay the 20" rims.
Air shock from Xfusion _ I just called the company and spoke with someone who sold the air shock to me. Worth the money
34-tooth cassette in back - there is little flat here
New platform pedals - no grip on the plastic ones

So - in all I spent a fair amount of money, but less than what I will spend on a new wheelset for me. I figure for 2+ years of use, plus the possibility of extending the use of hubs even longer, it is worth it to me.

Just picked one up for my 8 yo (he's a little small). Ive been holding off on upgrading his Performance Burnout. I plan to build some disc wheels, but I know that the rear would need a disc adaptor. I also plan on replacing the rear shifter and cassette (8sp). Disc brakes, better tires, and a riser bar. Lots of good info in this thread and elsewhere, but a few questions I have still are:
1. anyone find a good rear disc brake adaptor?
2. What are the rear shock dimensions, and how much do they cost?
Thanks for any help!

Ditched the stock tires in favor of Kenda Small Block 8s which lost an /amazing/ amount of weight. I'm hoping to get this bike under 20lbs once finished... going to be running 1x9, which should be MORE than enough. Too much fun.

Awesome Sashae. I've been geeking out on parts for building up my son's Spark JR 20 - plan is to give it to him as a Christmas present.
* I've identified some older 32-spoke disc hubs I have in my garage, and I plan to build them up with the stock rims
* I found the answer to my previous question about a rear disc adaptor and bought an A2Z DM-UNI adaptor from eBay. Also picked up some used F&R Elixir CR brakes (no discs) from eBay for $100. I've got extra (used) 160mm discs, but I might splurge for some 140mm ones.
* I plan to get some Small Block 8 tires
* I'll be pulling an 8-speed cassette and SRAM Rocket trigger shifter from my dirt-jump bike and plan to put it on this one - I might use the front chainguide as well.
* Next is the front crank/ring. I'm thinking Sinz 40mm from eBay, 32 ring, and re-using an old square taper BB that I should have in my garage (ps - anyone know the width? I'm guessing 68mm...)

Well looks like we are all in the same boat. Is the suspension on the scott Jr set up accurately for a 55 pound child. I think full suspension is a great idea for a little one as long as it is made for their weight. Feel free to comment.

Does anyone know where I can buy shock X-fusion 02 R 125 mm to scott spark?
X-Fusion Shox-USA did not sell those any more.
Thanks.

I got it from them a year ago, and guy (John) said it was the last one they had around the office and they are not making them. Nice shock, real rebound with wide range. I wish they did not have that stupid Manitou eyelet size, as I can't use needle bearing shock mounts. Stock ones are quite sticky - especially for a light rider.

I got it from them a year ago, and guy (John) said it was the last one they had around the office and they are not making them. Nice shock, real rebound with wide range. I wish they did not have that stupid Manitou eyelet size, as I can't use needle bearing shock mounts. Stock ones are quite sticky - especially for a light rider.

I had the same problem with X-Fushion shock sticking on my son's Spark RC. I solved the problem by going to torontocycles.com & purchasing Ti shock bolts with low profile Ti lock nuts.The lock nut allows you to back off the torque slightly & this eliminated all the sticking. To loose & the shock moves/knocks, every once and while I have to give the lock nut a hair more torque to stop this, but its well worth it to eliminating the sticking. Its going back a couple of year now, but I remembering having to buy the shock bolts too long for what I needed in order to get the correct shoulder length, which is important. I then cut the bolt to the correct length.Also ran a washer only on the locknut side.
If he doesn't have the right shock bolt shoulder length then I may have just bought Ti allen bolts to get the correct shoulder. If you're considering this let me now & I'll try & find the purchase order.

I had the same problem with X-Fushion shock sticking on my son's Spark RC. I solved the problem by going to torontocycles.com & purchasing Ti shock bolts with low profile Ti lock nuts.The lock nut allows you to back off the torque slightly & this eliminated all the sticking. To loose & the shock moves/knocks, every once and while I have to give the lock nut a hair more torque to stop this, but its well worth it to eliminating the sticking. Its going back a couple of year now, but I remembering having to buy the shock bolts too long for what I needed in order to get the correct shoulder length, which is important. I then cut the bolt to the correct length.Also ran a washer only on the locknut side.
If he doesn't have the right shock bolt shoulder length then I may have just bought Ti allen bolts to get the correct shoulder. If you're considering this let me now & I'll try & find the purchase order.

This does sound like a plan? I think M8x75 should work - I will measure. I will also get the Manitou heavy duty mounting kit.

I think they did it on purpose as the stock shock has no damping whatsoever.

P.S. Looks like a good idea with the sandpaper on pedal axles. Will go get the scraps back out of trash from the skateboard grip I was installing yesterdays.

I just ordered this dumper KS from Taiwan, and now I'm waiting for it.
I'll try to write about it.
Weight of the bike is slowly coming up to 9 kg.

I found the product information page for A5-RE. Apparently it is a friction damper. No oil.

A5-RR1 version adds a topout adjustment. It would be about 180g weight saving compared to the coil, if I remember correctly.

But realistically, for the amount of travel, and stiction in suspension, not much damping is needed. I keep X2 fully open.

There is 5.5x1.0 Fox. I wonder if it could be made to work by flipping the link and adding a 5mm internal shim (or making it 100mm rear travel). By looking at the picture it seems that rotating the link backwards will easily add about an inch eye to eye distance.

I found the product information page for A5-RE. Apparently it is a friction damper. No oil.

A5-RR1 version adds a topout adjustment. It would be about 180g weight saving compared to the coil, if I remember correctly.

But realistically, for the amount of travel, and stiction in suspension, not much damping is needed. I keep X2 fully open.

There is 5.5x1.0 Fox. I wonder if it could be made to work by flipping the link and adding a 5mm internal shim (or making it 100mm rear travel). By looking at the picture it seems that rotating the link backwards will easily add about an inch eye to eye distance.

Well, I do have Xfusion, so will not really try..

Axe, I don't think you can flip the links. I remember someone complaining of the air can being dented by the cable stop ( you can see it on my son's Spark a few posts up), I had suggested the links got flipped by accident and that was his problem.

Axe, I don't think you can flip the links. I remember someone complaining of the air can being dented by the cable stop ( you can see it on my son's Spark a few posts up), I had suggested the links got flipped by accident and that was his problem.

I think he flipped it upside down, so that the axle is higher. I suggest flipping it backward, so that the axle is further away, so that a shock with a 140mm e2e distance fits (not sure what would be the actual distance). such shock will have 25mm stroke, which can be shimmed easily to 20 (or whatever frame allows).

You can also dremel away the cable stop in a minute. I did it, partially, to run full length raillery and disk brake housing.

Hi,
I just installed a rear shock A5 KS to spark 20
Suitable bushes from coil stock shock.
It weighs 170 g with mounting bushes.
The stock coil shock weighs 290 g (with bushes)
KS A5 it is a friction damper - it is loud. Works like poof, zzzzz, poof, zzzz
Dumping is not sufficient. It works as a stock coil shock without dumping with pogo effect.

X-Fusion 02 from spark 24 is much better (I have one in spark RC)
It is difficult for me to write, I do not know English well.

Thanks Heckler11 - your English was good enough to get the point! It sounds like the A5 KS sucks. I plan to stick with the stock shock until I can come up with something better like a used X-fusion that shows up on Ebay or something. Thank you for the write up.

Thanks Heckler11 - your English was good enough to get the point! It sounds like the A5 KS sucks. I plan to stick with the stock shock until I can come up with something better like a used X-fusion that shows up on Ebay or something. Thank you for the write up.

I will try measuring today what flipping the link gets. Shimmed 140 x 25 stroke Fox would probably be a better choice if it can be fitted. I may have an XFusion for sale then...if I can get more then half price of the cheapest new old stock 140x25 I can find.